The present invention relates to a swash plate type variable displacement compressor.
Japanese Patent Application Publication No. H05-172052 discloses a conventional swash plate type variable displacement compressor (hereinafter referred to as compressor). The compressor has a housing including a front housing, a cylinder block and a rear housing. The housing has therein a suction chamber, a discharge chamber, a swash plate chamber and a plurality of cylinder bores, and a drive shaft is rotatably supported in the housing. The swash plate chamber has therein a swash plate that is supported on the drive shaft for rotation therewith. A link mechanism is provided between the drive shaft and the swash plate that permits changing of the inclination angle of the swash plate, that is, an angle of the swash plate relative to an imaginary plane extending perpendicularly to the axis of the drive shaft. A piston is reciprocally slidably received in each cylinder bore. Each piston has a pair of shoes that functions as part of a conversion mechanism converting the rotation of swash plate into reciprocating motion of the piston in the cylinder bore with a length of stroke that is determined by the inclination angle of the swash plate. The compressor further has an actuator that can change the inclination angle of the swash plate by changing the volume of a control pressure chamber formed in the actuator, and a control mechanism that controls the actuator.
The drive shaft has mounted thereon a first connecting member, a second connecting member, a thrust bearing and a moving member which are disposed in this order as seen toward the rear of the compressor. The first connecting member and the second connecting member cooperate to form a link mechanism. Although it is not clear from the above-cited Publication, it is thought that the contact between the first connecting member and the swash plate determines the maximum inclination angle of the swash plate. The second connecting member is rotatable with the drive shaft and movable in the axial direction of the drive shaft. The moving member is not rotated with the drive shaft but movable in the axial direction of the drive shaft. A thrust bearing is provided between the second connecting member and the moving member to support the thrust force.
The actuator is disposed in the rear housing and has a pressure control chamber. Pressure in the pressure control chamber causes the moving member to move in the axial direction of the drive shaft. The cylinder block has on the rear side thereof an axial hole and the second connecting member, the thrust bearing and the actuator are accommodated in the axial hole. The moving member has in the outer peripheral surface thereof an O-ring which is in slide contact with the axial hole of the cylinder block.
When the pressure of refrigerant in the discharge chamber is introduced into the pressure control chamber by the control mechanism and the pressure in the control chamber is increased, the moving member pushes the second connecting member in the direction that increases the inclination angle of the swash plate. As a result, the discharge volume per rotation of the drive shaft, i.e. the displacement of the compressor, is increased. When no discharge pressure is introduced into the pressure control chamber of the actuator, on the other hand, the pressure in the pressure control chamber is gradually reduced and the moving member ceases to push the second connecting member, with the result that the inclination angle is decreased. Accordingly, the displacement of the compressor is reduced.
The compressor needs to be so configured that parts of the compressor are assembled with a thrust allowance in the axial direction, taking into account the ease and efficiency in the assembly in actual production of the compressor.
The cylinder bore of the above compressor includes first and second cylinder bores that are formed in a single cylinder block on the opposite sides thereof. In some compressors, the cylinder block may include a first cylinder block having therein the first cylinder bore and a second cylinder block having therein the second cylinder bore, and the first cylinder block and the second cylinder block cooperate to form therebetween a swash plate chamber. In the compressor having such first and second cylinder blocks, a first thrust bearing may be provided between the first cylinder block and the drive shaft so as to receive a first thrust force acting on the drive shaft in one direction when the cylinder blocks are fastened together for assembling and a second thrust bearing may be provided between the second cylinder block and the drive shaft so as to support a second thrust force acting on the drive shaft in the opposite direction when the cylinder blocks are fastened together.
The aforementioned thrust allowance is a dimensional difference between the total length of parts as measured in the axial direction of the drive shaft before assembling and a depth of the thrust in the compressor after assembly. The total length of the parts as measured in the axial direction before assembly corresponds to the sum of the thicknesses of the first thrust bearing, the thickness of the second thrust bearing and the length of the drive mechanism of the compressor as measured in the axial direction. The drive mechanism refers to a link mechanism and the actuator located between the first thrust bearing and the second thrust bearing. The depth of the thrust in the assembled compressor corresponds to the length between the outer end surface of the first thrust bearing and the outer end surface of the second thrust bearing.
If the thrust allowance becomes excessive, the compressor may have problems such as deformation of the first and second cylinder blocks, increased torque for driving the drive shaft and shortened life of the first and second thrust bearings. This may cause deterioration of product yield in mass production of the compressor. If the thrust allowance is controlled strictly, parts for the compressor need to be subject to strict dimension control, thus increasing the production cost of the compressor. Especially, in the compressor according to the present invention having a complex drive shaft mechanism between the first thrust bearing and the second thrust bearing, as compared with, for example, the double-headed piston type swash plate compressor disclosed in the above Publication, strict dimensional control is imposed on the parts of the compressor.
Furthermore, parts of the compressor need to be manufactured under strict dimensional control for the maximum inclination angle of the swash plate to be set accurately and uniformly, which increases the production cost of the compressor.
The present invention, which has been made in light of the above-mentioned problems, is directed to providing a swash plate type variable displacement compressor that permits reduction of the production cost of the compressor.